Modern aircraft and particular commercial passenger aircraft have pressurized cabins that reduce the effective altitude within the aircraft while flying at higher altitudes. When an aircraft's cabin and flight deck effective altitude is reduced, the total pressure of the interior of the aircraft is increased. This leads to a higher differential pressure between the inside and outside of the aircraft with the stress becoming greater as the differential pressure increases. In order to reduce the altitude in this classical sense, either the structure of the aircraft would need to be redesigned or adjusted to safely withstand the higher pressure, or the aircraft is flown at a lower altitude. Although newer aircraft models whose fuselages are largely made of composite can withstand a higher differential pressure and in turn can handle a lower cabin and flight deck pressurized altitude, the effective altitude within the aircraft can be realized, without increasing the total pressure, by increasing the oxygen partial pressure to an equivalent lower altitude value.
Many commercial and other aircraft are equipped with nitrogen generating systems to generate nitrogen enriched air that is channeled into parts of the aircraft, such as fuel tanks, for creating an inert atmosphere. The nitrogen generating system also produces oxygen enriched air. However, the oxygen enriched air from the nitrogen generating system is dumped overboard and provides no further function to the aircraft. The nitrogen generating system receives bleed air flowing from at least one engine of the aircraft. During all phases of flight, a large portion (even majority) of the bleed air flow used in the nitrogen generating system is discarded in the form of oxygen enriched air. This bleed air flow is taken from the engine reducing its efficiency and thrust.